In general, the term “porous organic-inorganic hybrid materials” is also referred to as “porous coordination polymers” [Angew. Chem. Intl. Ed., 43, 2334 (2004)] or “metal-organic frameworks” [Chem. Soc. Rev., 32, 276 (2003)].
The porous organic-inorganic hybrid materials have been recently further developed through the integration of molecular engineering and material science. Said material(s) has a large surface area and pores of molecular size or nano size, and thus can be used not only for adsorbents, gas storage materials, sensors, membranes, functional thin films, drug delivery materials, catalysts, catalyst carriers, etc., but also for encapsulating guest molecules smaller than their pore size or separating molecules according to the sizes of the molecules by using their pores. Thus, said material(s) has recently been actively studied.
Particularly, porous organic-inorganic hybrid materials with crystallinity can be defined as porous organic-inorganic polymer compound(s) having a central metal ion bonded to an organic ligand. The term porous organic-inorganic hybrid materials with crystallinity also refer to a crystalline compound with pores of a molecular size or nano size, including both organic material and inorganic material in its framework structure.
Porous organic-inorganic hybrid materials have usually been prepared by a solvothermal synthesis, but a hydrothermal synthesis including adding acid in order to increase the hydrothermal stability has also been used. As representative porous organic-inorganic hybrid materials prepared by the hydrothermal synthesis, Cr3O(H2O)2F[C6H3—(CO2)3]2.nH2O (n˜14.5), Fe3O(H2O)2F[C6H3—(CO2)3]2.nH2O (n˜14.5), and Cr3F(H2O)2O[C6H4(CO2)2]3.nH2O (n˜25) have been reported [Science 23, 2040, 2005; Chemical Communication 2820, 2007, Accounts of Chemical Research, 38, 217, 2005]. However, in the case of using hydrofluoric acid as a crystallization agent under high pressure as in the prior methods, in the selection of a reactor for scale-up process on preparing porous organic-inorganic hybrid materials, there is a severe limitation in selecting a reactor other than the Teflon reactor. In addition, the prior methods involve relatively high waste treatment costs. Recently, Korean Patent Application No. 2007-0063881 has disclosed a method for preparing porous organic-inorganic hybrid materials using a reaction solution including nitric acid, but not using hydrofluoric acid as a crystallization agent in prior methods for preparing porous organic-inorganic hybrid materials. However, methods for preparing porous organic-inorganic hybrid materials have to be carried out under high pressure of 3 atm or more. Particularly, the methods have to be carried out using a high concentration (5% or higher) of acid at high pressure (3 atm or more) and high temperature, and thus there has been a severe limitation in selecting a reactor.
Meanwhile, an adsorbent that can easily adsorb and desorb water has various uses. For example, a dehumidifier may utilize the adsorbent having a property of adsorbing water at low temperature and desorbing water when it is heated to high temperature. In addition, in case where an adsorbent is used in coolers/heaters, during heating operation, the adsorbent can act as a humidifier by adsorbing the outdoor moisture of low temperature, introducing the moisture to the indoor, and desorbing it in the indoor where the temperature is high; and during cooling operation, the adsorbent can achieve a comfortable indoor atmosphere by adsorbing the indoor moisture of low temperature, taking it to the outside and desorbing it in the outdoor where the temperature is high. Air-conditioners and humidity controllers applying such ideas have been suggested in U.S. Pat. Nos. 6,978,635, 6,959,875, 6,675,601, etc. However, the patents do not describe the adsorbent used in such devices in detail, but only mention that silica gel, zeolite, ion exchange resin are used, or that an adsorbent is used. In addition, such adsorbents not only have a low adsorption amount, but also cause the operation costs to rise by requiring a high temperature of at least 100° C. for desorption, etc.
Recently, Korean Patent No. 806586 has reported the case of using porous organic-inorganic hybrid materials capable of adsorbing and desorbing water even at low temperature. However, according to the patent, porous organic-inorganic hybrid materials have to be crystallized such that they have a surface area of at least 1,000 m2/g and a pore volume of at least 1.0 ml/g. Accordingly, the technology requires an additional purification process, which leads to very high manufacturing costs.
Therefore, it is necessary to develop an adsorbent that can desorb even at low temperature and has a large difference between the adsorption amount and the desorption amount by an economical process. However, there have always been problems that in case the adsorption amount is high, desorption is difficult, and in case the adsorption amount is low, the difference between the adsorption amount and the desorption amount is small.
In addition, until now, Activated carbon and hydrophobic zeolite have been mainly used as adsorbents that can remove organic compounds present in an indoor space. Activated carbon has a very large surface area due to a number of nano pores, and has a strong adsorption strength to non-polar molecules, and thus has an excellent effect in removing exhaust gas, removing smell and odor, whereas zeolite is a hydrophilic adsorbent having a pore diameter of about 3-10 Å and thus has a strong adsorption property to carbon monoxide, carbon dioxide and water. However, most adsorbents only have hydrophobic or hydrophilic properties, and thus have disadvantages that they cannot effectively adsorb and remove volatile organic compounds including water.
Accordingly, the present inventors developed porous organic-inorganic hybrid materials with crystallinity having uniform particle sizes, obtained under the synthesis conditions of a low pressure of 3 atm or less and high concentration (the molar ratio of solvent to metal precursor is 100 or less). The present inventors confirmed that an adsorbent including said porous organic-inorganic hybrid materials with crystallinity can easily adsorb and desorb water even at low temperature, and thus can be used as a water adsorbent, heat pump, desiccant, adsorbent/desiccant for sewage treatment, adsorbent for a refrigerating machine, and adsorbent for an air conditioner or cooler, and the present inventors also confirmed that an adsorbent including said porous organic-inorganic hybrid materials with crystallinity has excellent adsorption properties to volatile organic compounds (VOCs) as compared with conventional adsorbents. Thereby, the present inventors achieved the present invention.